High-frequency electron discharge tube system



(5. DIEMER June 23, 1953 HIGH-FREQUENCY ELECTRON DISCHARGE TUBE SYSTEM Filed March 25, 1950 &

INVE/VTDR GESINUS DIEMER AEA/T Patented June 23, 1953 HIGH-FREQUENCY ELECTRON DISCHARGE TUBE SYSTEM Ge'sinus Diemer, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application March 25, 1950, Serial No. 151,956

In the Netherlands March 29, 1949 2 Claims.

of the cathode consisting of a homogeneously porous sintered body made from one or more of the refractory metals tungsten, molybdenum, tantalum, hafnium and niobium, and the pores of the porous body constituting the largest apertures in the wall of the cathode body, and is an improvement in or modification of the invention described in U. S. A. Patent application Ser. No. 39,264, filed July 17, 1948, now Patent 2,543,728, issued February 27, 1951.

It has been found that the aforesaid cathodes have a satisfactory life even when highly loaded, in contra-distinction to the usual cathodes furnished with alkaline-earth oxide layers. With the usual cathodes commonly not more than 5% of the saturation current is used to reduce noise and variation in the characteristic curve. This noise suppression results from the space charge in the potential minimum between the cathode and the control grid or the anode in the case of a diode.

With very high radio frequencies, for example of the order of magnitude of 1000 mc./sec. and higher, the spacing between the cathode and the control grid should be very small in connection with transit time conditions, so-that the control grid approaches very closely to the potential minimum. Due to this the electrons reversing their direction in front of the potential minimum greatly contribute to noise damping and grid damping. Moreover, the noise suppression is much less effective than if the potential minimum is remote from the grid.

We have found, that the aforesaid disadvantages are avoided with the use of the aforesaid cathodes.

Accordin to the invention, in a device for amplifying, producing or modulating electrical oscillations having a frequency of the order of 1000 mc./sec. and higher, which comprises an electric discharge tube in which the cathode, of the type described in the aforesaid patent, contains a supply of alkaline earth metal compounds, at least part of the cathode-wall consisting of a homogeneously porous sintered body of one or more of the refractory metals tungsten, molybdenum, tantalum, hafnium and niobium and the pores of the porous body constituting the largest apertures in the wall of the cathode body, the discharge tube is so adjusted that in the absence of signal voltage at least of the 2 saturation current passes the potential minimum between the cathode and the control electrode, the spacing'between the cathode and the control electrode being smaller than 30 microns.

Since a larger part of the saturation current passes the potential minimum, the latter approaches more closely to the cathode and there are less returning electrons. For these two reasons there occurs less damping across the input circuit of the control electrode and, moreover, less noise. Since for the same output current the cathode is much smaller than usual the cathode-losses also are much smaller.

If the control electrode is a grid, there occurs less island effect than in the usual adjustment;

In a device according to the invention, the transit times and consequently also the transit time variation between grid and cathode are much smaller than in the usual devices, since the control voltage is higher.

In order that the invention may be readily carried into effect an example will now be described in detail with reference to the accompanyin drawing in which:

Fig. 1 is a diagrammatic view in cross-section of an electric discharge tube in accordance with the invention;

Fig. 2 shows a circuit diagram in which the tube shown in Fig. 1 may be employed.

Referring to Fig. 1, a high-frequency tube in accordance with the invention, a so-called lighthouse tube, comprises a cathode l, a control grid 2, and an anode 3. Each of the aforementioned electrodes I, 2, 3 are connected, respectively, to one of three planar electrodes 4, 5, 6 by which external circuit connection can be made thereto, for example, by means of concentric conductors. The planar electrodes are sealed directly into the wall 1 of the tube, which wall usually consists of glass. The cathode I, which is of the type described in the aforementioned patent, comprises a heating filament ID, a homogeneously, porous, sintered body H completely surrounding a supply l2 of alkaline earth metal compounds, and a support therefor l3.

A comparison will now be made between the device according to the invention, and a device comprising an oxide-coated cathode of the usual type. The oxide coated cathode in the latter type has a temperature of 750 C. and a saturation current of 3 amp./cm. The anode current is ma./cm. i. e. 5 of the saturation current. In the event of a cathode-grid spacing of 17 microns the potential minimum lies 4.5 from the grid.

The saturation current at a temperature of 900 C. of a cathode of the type referred to in patent application No. 39,264 and shown in 1 is 0.5 amp/c1212. If the anode current and the cathode-grid spacin are chosen to be the same as referred to above, 30% of the saturation current is consequently used. In this event, the potential minimum lies 8.5 microns from the grid, i. e. approximately double the value of the aforesaid case. In the first and second case the is 5.4 and 4.0 respectively apart from the island effect Which, in the second case, is undoubtedly much smaller, so that the decrease in mutual conductance tends to be immaterial. From the example given it appears that if a great part of the saturation current is used, the location of the potential minimum becomes more advantageous, whilst the excellent properties of the cathode referred to in the patent application Ser. No. 392% ensure a satisfactory In connection with the possibility of complete driving, 50% of the saturation current will generally not be exceeded in the static adjustment. Fig. 2 shows a simple circuit arrangement for the tube comprising the tube itself, including a cathode i, control grid 2, and anode 3, a source of supply voltage 28 for the tube, and an anode resistor 2i.

What I claim is:

1. An electron discharge tube system for eleetrical oscillations having a frequency of the order of 1000 megacycles per second and higher cornprisin an electron discharge tube having an incandescible cathode assembly comprising a structure forming internal cavity, the portion of the structure surrounding said cavity consisting of refractory metal, a supply of an allaline-earth metal compound in said cavity, and a homogeneously porous sintered body of refractory metal forming the emissive part oi the Wall of said structure, said structure being tightly closed with the pores of said body forming the largest apertures connecting the cavity to the outside of the structure, a grid electrode assembly positioned adjacent to said cathode and spaced therefrom a distance smaller than 30 microns, and an anode in spaced relationship to said grid and cathode assemblies, said discharge tube having a given saturation current value; and means to apply to said cathode and anode a potential having a value at which a current flow greater than about 10% of the said saturation current value is produced in said tube. a

2. An electron discharge tube system for electrical oscillations having a frequency of the order of 1000 megacycles per second and higher comprising an electron discharge tube having an incandescible cathode assembly comprising a structure forming an internal cavity, the portion of the structure surrounding said cavity consisting of refractory metal, a supply of an alkaline-earth metal compound in said cavity, and a homogeneously porous sintered body of a refractory metal selected from the group consisting of tungsten, molybdenum, tantalum, hafnium and niobium forming the emissive part of the wall of said structure, said structure being tightly closed with the pores of said body forming the largest apertures connecting the cavity to the outside of the structure, a grid electrode assembly arranged adjacent to said cathode and spaced therefrom a distance smaller than 30 microns, and an anode in spaced relationship to said grid and cathode assemblies, said discharge tube having a given saturation current value; and means to apply to said cathode and anode a potential having a value at which a current flow greater than about 20% of the said saturation current value is produced in said tube.

Ci-ILSINUS DIEIMER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,839,899 Slepian Jan. 5, 1932 2,121,589 Espe June 21, 1938 2,455,381 Morton et al Dec. '7, 1948 FOREIGN PATENTS Number Country Date 115,700 Great Britain May 21, 1918 

